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A Case of HIV Transmission on PrEP and Its Implications

March 15, 2016

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At the 2016 Conference on Retroviruses and Opportunistic Infections (CROI), David Knox, M.D., presented information about a case of HIV transmission in a man who had multiple sexual partners and who did not use condoms -- and who was taking pre-exposure prophylaxis (PrEP) in the form of daily Truvada.

In this CATIE News bulletin we review key details about this important case and its possible implications for HIV risk reduction in the future. For people at high risk for HIV infection who are considering initiating Truvada as PrEP to help reduce their risk, and for those currently taking PrEP, we present advice from doctors who are experienced with the use of Truvada as PrEP.

Although this is the first well-documented case of HIV transmission in someone who is highly adherent to Truvada as PrEP, it is not the first case of such a transmission. Therefore, for people using or considering initiating medicines to reduce their risk of acquiring HIV via sexual transmission, it is important to bear in the mind the points listed below.

Truvada -- which contains two anti-HIV drugs, tenofovir + FTC (emtricitabine) -- has helped reduce the risk of HIV infection in thousands of people. Risk reduction is greatest when Truvada is used exactly as directed -- as part of a package of measures that include the following:

  • screening for HIV and sexually transmitted infections (STIs) prior to initiating Truvada
  • treating any STIs that are detected
  • getting vaccinated against hepatitis B (if necessary), and potentially hepatitis A and human papillomavirus
  • the correct and consistent use of condoms
  • regular and frequent testing (at least every three months) for HIV and testing, and treatment if necessary, for other STIs


Case Details

A Toronto man in his early 40s who had tested negative for HIV and common STIs (syphilis, gonorrhea and chlamydia) sought Truvada as PrEP from his doctor in the spring of 2013. After assessment, blood tests and counselling, the man began taking Truvada every day exactly as directed. For the next two years he continued to be highly adherent and his screening for HIV was repeatedly negative.

In April 2015 the man complained of persistent and severe abdominal pain. As this was an issue that could be potentially serious, he was referred to the Emergency Room of a local hospital. Initially doctors did not suspect acute HIV infection because the patient said that he took Truvada every day exactly as directed. After a series of tests ruled out inflammatory bowel disease, in early May 2015 the man's doctor had his blood tested for HIV antibodies and an HIV protein called p24 antigen. The man tested positive for p24 antigen but negative for HIV antibodies, which is consistent with early HIV infection. 

Fearing the possibility that his patient was undergoing very early HIV infection, Dr. Knox prescribed anti-HIV therapy as follows:

  • the protease inhibitor darunavir (Prezista)
  • a small dose of the protease inhibitor ritonavir (Norvir), which raises and prolongs the level of darunavir in the body
  • the integrase inhibitor raltegravir (Isentress)

Truvada was continued, as this drug could have potentially provided additional antiviral activity when combined with the other drugs.

Confirming Adherence

The man's doctor knew that it was important to assess the patient's adherence to Truvada. So, with the limited blood samples available to him (the vast majority of family doctors do not have the high-level facilities to store blood and other fluid samples that are standard in research labs), he had a tiny portion of these samples undergo sophisticated analysis in a research laboratory in Vancouver under the supervision of virologist Richard Harrigan, Ph.D., at the BC Centre for Excellence in HIV/AIDS. Specifically, these analyses assessed the levels of the drugs that are in Truvada -- tenofovir and FTC.

Another way of assessing adherence, though less direct, is to check pharmacy records of when the patient refilled his prescriptions. In large analyses done in B.C., timely re-filling of prescriptions has been found to be highly associated with good adherence (and good clinical outcomes) among people who take anti-HIV medicines.

The analyses of the patient's blood taken from early May 2015 were similar to what has been done in some large clinical trials in which Truvada was used as PrEP. Researchers in B.C. found that the levels of tenofovir in the patient's blood were very high and indicated that he had been adherent to Truvada for a long time. Other, more sophisticated tests (mass spectrometry) confirmed that the patient's blood contained very high levels of tenofovir and FTC. Thus, there is no doubt that the patient was taking Truvada for quite some time, exactly as directed.

Focus on the Strain of HIV

Prior to these blood tests that sought to assess the patient's adherence, the man had not taken other anti-HIV medicines apart from Truvada. However, genetic analysis of the virus with which he was now infected revealed a strain of HIV that was unusual -- it had changes, or mutations, in its genetic makeup that allowed it to partially or wholly resist many treatments. Such mutations generally arise because medicines have not been taken exactly as directed.

Below we list by drug classes the treatments to which his strain of HIV could be resistant:

Nukes (Nucleoside Analogues)

  • two-fold reduced susceptibility to abacavir (Ziagen)
  • 1.3-fold reduced susceptibility to tenofovir (Viread and in Truvada)
  • high-level resistance to 3TC (lamivudine)
  • high-level resistance to FTC (in Truvada)

The specific mutation that confers resistance to 3TC and FTC is called M184V. We will discuss the significance of this mutation later in this bulletin.


  • resistance to nevirapine (Viramune)

Integrase Inhibitors

  • reduced susceptibility to raltegravir (Isentress)
  • resistance to elvitegravir (in Genvoya and Stribild)

Furthermore, laboratory testing with cells infected with this strain of HIV and different concentrations of drugs confirmed the genetic analysis.


The amount of HIV in the man's blood was relatively low: 28,000 copies/mL in early May 2015.

Four weeks after blood tests first suggested HIV infection and about three weeks after initiation of treatment, his viral load fell to less than 50 copies/mL. Once this occurred, given the genetic and other analyses of resistance, and to avoid the possibility of HIV becoming resistant to the drugs he was currently taking, Dr. Knox changed the man's treatment to the following combination:

  • dolutegravir (Tivicay)
  • darunavir + cobicistat (this latter drug raises and maintains levels of darunavir in the body; both drugs are sold in one pill called Prezcobix)
  • rilpivirine (Edurant)

Thus, due to the strain of multidrug-resistant HIV (MDR-HIV) with which he was infected, the man was placed on a complex regimen of anti-HIV drugs. Such regimens are usually associated with side effects, yet Knox told us that these drugs were "remarkably well tolerated" by his patient.

Mutations and Their Discontents

The cluster of mutations present in the man's strain of MDR-HIV are unusual and suggest that the person who transmitted this strain had been exposed to older anti-HIV drugs in the past that are not commonly used today in routine HIV care in Canada and other high-income countries. These older drugs included the following:

  • AZT (zidovudine, Retrovir)
  • d4T (stavudine, Zerit)
  • nevirapine (Viramune)

However, the virus also had resistance to the integrase inhibitor elvitegravir; this drug only came into use in Canada and other high-income countries in about 2012.

This cluster of mutations in the man's virus is rare. Dr. Harrigan estimates that less than 1% of HIV-positive Canadians who have a persistently detectable viral load have such a strain.

However, there are other aspects of this case and drug-resistant mutations that are concerning, and we explore those next.

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This article was provided by Canadian AIDS Treatment Information Exchange. It is a part of the publication CATIE News. Visit CATIE's Web site to find out more about their activities, publications and services.

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Please note: Knowledge about HIV changes rapidly. Note the date of this summary's publication, and before treating patients or employing any therapies described in these materials, verify all information independently. If you are a patient, please consult a doctor or other medical professional before acting on any of the information presented in this summary. For a complete listing of our most recent conference coverage, click here.


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